The present invention is generally directed to electronic control circuitry and, more specifically, to a system and method that utilizes a differential current mirror system to achieve process-voltage-temperature compensated current splitting for variable gain control.
Current mirrors are commonly used as electronic control circuits in integrated circuits. When a reference current is provided as an input to a current mirror, the current mirror provides an output current that is identical (or proportional) to the reference current. The term xe2x80x9ccurrent mirrorxe2x80x9d reflects the fact that the output current is a xe2x80x9cmirror imagexe2x80x9d of the input reference current.
The difference between two current input signals is referred to as the differential mode of the two current input signals. The average value of two current input signals is referred to as the common mode of the two current input signals. In many applications input current signals may be represented as a linear combination of a differential mode component and a common mode component of the current input signals. It is often desirable to amplify the differential mode component by a large gain factor, while minimizing the amplification factor of the common mode component. Minimizing the amplification factor of the common mode component is referred to as xe2x80x9crejectingxe2x80x9d the common mode component.
Prior art differential current mirrors are capable of providing two output currents that are identical (or proportional) to two input reference currents. However, prior art differential current mirrors are not capable of rejecting the common mode component of input current signals.
Variable gain control is desirable in many types of electronic control circuits. For example, in an adaptive equalization filter it is desirable to be able to vary the amount of gain within the filter to compensate for variations in the transmission channel. Additionally, it is desirable to be able to vary the amount of gain within the filter to compensate for changes within the circuit components caused by process-voltage-temperature (PVT) variations.
There is therefore a need in the art for a differential current mirror system (1) that is capable of rejecting common mode input current signals and (2) that is capable of splitting an input current into two portions to provide signals for varying the amount of gain within a control circuit.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a differential current mirror system for providing differential output current signals (1) in which common mode current signals are rejected, and (2) in which an input current signal is split into two portions to provide signals for varying the amount of gain within a control circuit.
The differential current mirror of the present invention comprises a pair of diode connected transistors and a differential amplifier. In an advantageous embodiment of the present invention, the pair of diode connected transistors and the differential amplifier comprise MOSFET transistors. The pair of diode connected transistors comprises a first transistor and a second transistor coupled together. The differential amplifier comprises a third transistor and a fourth transistor in which the gate of the third transistor receives a first input current signal from the drain of the first transistor and in which the gate of the fourth transistor receives a second input current signal from the drain of the second transistor.
It is an object of the present invention to provide a differential current mirror that provides common mode rejection of current signals.
It is another object of the present invention to provide a common mode rejection differential current mirror that provides power supply rejection at the output.
It is still another object of the present invention to provide a common mode rejection differential current mirror with a mirroring ratio that is independent of process-voltage-temperature (PVT) variations in the electronic components of the system.
It is yet another object of the present invention to provide a common mode rejection differential current mirror that can operate at low voltages.
The current splitting circuit of the present invention splits an input current into a first current portion that is proportional to a first scale factor that has a value between zero and one. The remainder of the current is a second current portion that is proportional to a second scale factor that has a value that is equal to one minus the first scale factor.
It is an object of the present invention to provide a current splitting circuit that is capable of splitting an input current into two portions to provide signals for varying the amount of gain within a control circuit.
It is also an object of the present invention to provide a current splitting circuit that is capable of providing signals for varying the amount of gain within a control circuit in a manner that is very accurate and independent of process-voltage-temperature (PVT) variations in the electronic components of the system.
It is also an object of the present invention to provide a current splitting circuit that can operate at low voltages.
It is also an object of the present invention to provide a current splitting circuit that is capable of providing variable gain control signals in an adaptive equalization filter.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9cor,xe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.